1. Technical Field
The present invention relates to a lighting apparatus, a filter apparatus and an image display suitable medical application, particularly to, a lighting apparatus, a filter apparatus and an image display which improve identification of living body tissues.
2. Description of Related Art
As lighting used in the medical field and so on, a shadowless lamp or astral lamp which does not cast a shadow under the light is used in general. As such a shadowless lamp, a high luminance lamp such as xenon lamp, halogen lamp and metal halide lamp with color temperature near sunlight is used (for example, Japanese Patent Laid-Open Publication TOKUKAI No. 2003-339738). However, it is important not only to provide shadowless effect but also easy identification of living body tissues for medical lighting. That is, it is desirable that the spectrum components of reflected light provide the component with heightened contrast of living body tissues. For example, a light source which provides sufficient color difference to identify an artery and a vein during an operation is required in a medical application.
On the other hand, in recent years, dissimilarly to an electric bulb such as an incandescent lamp which emits light with heat energy by heating the metal filament to the incandescence state with an electric current applied thereto, a lighting apparatus which employs a semiconductor light emitting element transforming electrical energy into electromagnetic radiation by using a semiconductor, or a light emitting device converting wavelength of light emitted from such a semiconductor light emitting element in combination with a phosphor has been developed. Particularly, a light emitting device using a nitride group semiconductor, such as gallium nitride, can emit ultraviolet light, blue light, green light, and soon. The device is high efficient and low power consumption, and in addition can be small, has resistance against mechanical vibration and so on, has a long life, and has high reliability. Since the device has these advantages, it is capable of being used in various applications. However, this type of semiconductor light emitting device generally has reflection spectrum components different from an electric bulb or sunlight. Accordingly, there is a problem that such a device is not suitable for a medical application. For example, when a white LED is used as medical lighting, it is difficult to identify an artery and a vein.